Circuit element utilizing semiconductive materials



ALS

une W. SHOCKLEY CIRCUIT ELEMENT UTILIZING SEMICONDUCTIVE MATERI 3sheets-smet 1 Original F'iled June 26, 1948 Fla 4 ATTORNEY June 22, 1954w. sHocKLEY 2,581,993V

CIRCUIT ELEMENT UTILIzING sEMIcoNDucTIvE MATERIALS 3 Sheets-Sheet 2Original Filed June 26, 1948 /NVE/vro@ By. W. .SHOE/(L E Y ATTO/PNE? W.SHOCKLEY June 22; 1954l CIRCUIT ELEMENT UTILIZING SEMICONDUCTIVEMATERIAL original Filed June 2e, 194e 3 Sheets-Sheet 3 /NVENTOR BV W.SHOCK/ EY Patented June 22, 1954 oiaoorr ELEMENT U'rILIzING SEMICON-lnnorlvn MATERIALS William Shockley, Madison, N. 3., assigner to BellTelephone Laboratories,

Incorporated,v New York, N. Y., a corporation of New York Originalapplication 8 Claims. l

This application is a division of application Serial No. 35,423, ledJune 26, 1948, now Patent 2,569,347, granted September 25, 1951, forCircuit Element Utilizing Semiconductive Materials. Y This inventionrelates to means for and methods of translating or controllingelectrical signals and more particularly to circuit elements utilizingsemiconductors and to systems including such elements.

f One general object of this invention is to provide new and improvedmeans for and methods .of translating and controlling, for exampleamplifying, generating, modulating, intermodulating orconverting,electric signals.

Another general object of this invention is to enable the efiicient,expeditious and economic translation or control of electrical energy.

In accordance with one broad feature of this invention, translation andcontrol of electric signals is effected by alteration or regulation ofthe conduction characteristics of a semiconductive body. Morespecifically, in accordance with one broad feature of this invention,such translation ,and control is effected by control of thecharacteristics, for example the impedance, of a layer or barrierintermediate two portions of a semiconductive body in such manner as toalter advantageously the flow of current between the two portions.

One feature of this invention relates to the .control of current flowthrough a semiccnductive body by means of carriers of charge ofopposite. sign to the carriers which convey the current through thebody. v

Another feature of the invention pertains to ,controlling the currentflowing through a semiconductive body by an electrical eld or fields inaddition to those responsible for normal current iiow through the body.

An additional feature of this invention relates to a body ofsemiconductive material, means for making electrical connectionrespectively to two portionsrof said body, means for making a thirdvelectrical connection to another portion of the body intermediate saidportions and circuit means including power sources whereby the influenceof the` third connection may be madeto `control the flow of currentbetween the other connections.

, Another feature pertains to a semiconductive body comprisingsuccessive zones of material of opposite conductivity type eachseparated from `theother byan electrical barrienmeans for makingexternal connection respectively to` two of said zeneaand means ,formaking other. 09111180" Divided and 1949, Serial No. 91,594

June 26, 1948, Serial No. this application May 5,

(Cl. Z50-$6) 2 tions intermediate to the two for controlling the :dow ofcurrent across one or more of the electrical barriers.

A further feature resides in a body of semiconductive materialcomprising two zones of material of opposite conductivity type separatedby a barrier, means for making external electrical connectionsrespectively to each zone and means for making a third connection to thebody at the barrier for controlling the flow of current between theother two connections.

An additional feature pertains to a semiconductive body comprising twozones of material of like conductivity type with an intermediate zone ofmaterial of opposite conductivity type, the zones being separatedrespectively by barriers, means for making electrical connectionsrespectively to the two zones, and means for making a third connectionto the intermediate zone for controlling the effectiveness of a barrierto thereby control the flow of current between the zones of likematerial.

Another feature of this invention involves a semiconductive body whichmay be used for voltage and power amplification when associated withmeans for introducing mobile carriers of charge to the body atrelatively low voltage and extracting like carriers at a relatively highVoltage.

A further feature of the invention involves creation of voltage andbarrier conditions adjacent an output connection or point of extractionof current whereby current amplification in addition to voltageamplification may be obtained.

Other objects and features of this invention will appear more fully andclearly from the following description of illustrative embodimentsthereof taken in connection with the appended drawings in which:

Fig. 1 shows in section one embodiment of the invention with anappropriate circuit;

Fig. 2 shows in section another embodiment of the invention withillustrative circuit connections; O

Fig. 3 shows vin section an embodiment somewhat similar to lthat of Fig.2 with certainV structural differences and with a suitable circuitarrangement; t

Figs. 3A and 3B show in fractional sections modications of Fig. 3v;

Fig. 4 shows insection a modification of Fig. 3 in which an embeddedelectrode .is used;

Fig. 5 shows in fractional section aV further modification of the typeof device shown in Fig. 4 and including features of AVdetailalsoapplicable vto other embodiments; Y

Fig. 6 shows an embodiment of the invention similar to that illustratedin Fig. 3 with a diilerent arrangement for making connection to part ofthe device;

Fig. 7 shows an assembled slab structure embodying some particularstructural details;

Fig. 8 shows, with an appropriate circuit, a sectional view of anembodiment of the invention having more than one control portion;

Fig. 9 shows in section a device similar to that of Fig. 8 with adifferent circuit arrangement.

Fig. 10 shows a two-electrode device otherwise similar to that of Fig.3, adaptable as a transit time diode with energy level diagrams usefulin explaining its operation;

Fig. 11 is a diagrammatic showing of curves associated with circuitelements to aid in explaining certain principles of the invention;

Fig. 12 is a diagrammatic showing similar to that of part a of Fig. 11to illustrate the effect of using diierent materials for certain partsof the devices contemplated by the invention; and

Fig. 13 is a diagrammatic illustration of conditions in the outputportion of devices made in accordance with current amplifying featuresof the invention.

As an aid to a full understanding of the description hereinafter ofspecific embodiments of the invention, a brief discussion of somepertinent principles and phenomenon, and an explanation of certain termsemployed in the description is in order.

As is known, see for example, Crystal rectifiers by H. C. Torrey and C.A. Whitmer, volume 15 of the M. I. T. Radiation Laboratories series,there are two ykinds of semiconduction, referred to an intrinsic andextrinsic. Although some of the semiconductive materials contemplatedwithin the purview of this invention may exhibit both these kinds ofsemiconduction, the kind referred to as extrinsic is of principalimport.

Semiconduction may be classiiied also as of two types, one known asconduction by electrons or the excess process of conduction and theother known as conduction by holes or the defect process of conduction.The term holes, which refers to carriers of positive electric charges asdistinguished from carriers, such as electrons, of negative charges willbe explained more fully hereinafter.

Semiconductive materials which have been found suitable for utilizationin devices of this invention include germanium and silicon containingminute quantities of signicant impurities which comprise one way ofdetermining the conductivity type (either N- or P-type) of thesemiconductive material. The conductivity type may also be determined byenergy relations with in the semiconductor. For a more detailed-explanation reference is made to the application 'of J. Bardeen and W.H. Brattain Serial No. 33,466, led June 17, 1948, now Patent 2,524,035,granted October 3, 1950.

The terms N-type and P-type are applied to semiconductive materialswhich tend to pass cur-- rent easily when the material is respectivelynegative or positive with respect to a conductive contact thereto andwith difficulty when 'the reverse is true, and which also haveconsistent Hall and thermoelectric effects.

The expression significant impurities is here used to denote thoseimpurities which affect the electrical characteristics of the materialsuch as its resistivity, photosensitivity, rectification, and the like,as distinguished from other imr of the basic material in the puritieswhich have no apparent effect on these characteristics. The termimpurities is intended to include intentionally added constituents aswell as any which may be included in the basic material as found innature or as commercially available. Germanium and silicon are suchbasic materials which, along with some representative impurities, willbe noted in describing illustrative examples of the present invention.Lattice defects such as vacant lattice sites and interstitial atoms wheneffective in producing holes or electrons are to be included in signingcant impurities.

In semiconductors which are chemical compounds, such as cuprous oxide orsilicon carbide, deviations from stoichiometric compositions and latticedefects, such as missing atoms or interstitial atoms, may constitute thesigniiicant impurities.

Small amounts of impurities, such as phosphorus in silicon, and antimonyand arsenic in germanium, are termed donor impurities because theycontribute to the conductivity of the basic material by donatingelectrons to an uniii-led conduction energy band in the basic material.The donated negative electrons in such a case constitute the carriers ofcurrent and the material and its conductivity are said to be of theN-type. This is also known as conduction by the excess process. Smallamounts of other impurities, for example boron in silicon or aluminum ingermanium, are termed acceptor impurities because they contribute to theconductivity by accepting electrons from the atoms iilled'band Such anacceptance leaves a gap or hole in the filled band. By interchange ofthe remaining electrons in the filled band, these positive holeseffectivelyv move about and constitute the carriers of current, and thematerial and its conductivity are said to be of the P-type. The termdefect process may be applied to this type of conduction.

Methods of preparing silicon of either conductivity type or a body ofsilicon including both types are known. Such methods are disclosed inthe application oi J. H. Scarf and H. C. Theuerer filed December 24,1947, Serial No. 793,744 now Patent 2,567,970, granted September 18,1951 and United States Patents 2,402,661 and 2,402,662 to R. S. Ohl.Such materials are suitable for use in connection with tlie presentinvention. Germanium material may also be made in either conductivitytype or in bodies containing both types and it may be so treated as toenable it to withstand high voltages in the reverse direction from therectification viewpoint. This material may be prepared in accordancewith the process disclosed in the application of J. H. Scaf and H. C.Theuerer filed December 29, 1945, Serial No. 638,351, now Patent2,602,211, granted July 8, 1952. Bodies of semiconductive material foruse in the practice of this invention may also be prepared lby pyrolyticdeposition of silicon or germanium with suitable significant impurities.Methods of preparation are outlined in United States patentyapplications lof K. H. Storks and G. K. Teal, Serial No. 496,414, filedJuly 28, 1943, now Patent 2,441,603, granted May 18, 1948; G. K. TealSerial No. 655,695, filed March 20, 1946, now Patent 2,556,991 grantedJune 12, 1951; and G. K. Teal Serial No. 782,729, led October 29, 1947,now Patent 2,556,711, granted June 12, 1951.

The term barrier or electrical barrier used inthe description anddiscussion of devices in accordance with this invention is applied to ahigh resistance interfacial condition between contacting semiconductorsof respectively opposite conductivity types or between a semiconductorand a metallic conductor whereby current passes with relative ease inone direction and with relative diiiiculty in the other.

-The devices to be described are relatively small which hasYnecessitated some exaggeration of proportions in the interest ofclarity in the illustrations which are mainly or essentiallydiagrammatic. This is particularly true of the intermediate orintervening layers which are usually very thin. In some cases thislayer, e. g., the P-layer in Fig. 11, has been shown wider than theflanking N-layers in order that the accompanying energy level diagramsmay be more clearly shown. The dimension in the direction perpendicularto the paper may vary in accordance with the cross-sectional arearequired.

The device shown in Fig. 1 comprises a body or block of semiconductivematerial, for example germanium, containing significant impurities. Theblock comprises two zones Ill and IIV respectively of N- and P-typematerials separated by the barrier I2. The opposite ends of the blockare provided with connections I3 and I4 which may be metallic coatings,such as cured silver paste, a vapor-deposited metal coating or the like.

Means for making connection to the barrier region of the block comprisea drop of electrolyte i such as glycol borate in which is immersed awire loop I6, or other suitable means, such as a disc of metal.

Conductor I'I leads from connection I4 to a load RL and thence through apower source, such as battery I8, and back via conductor IS to the bodyat connection I3. A source 2l of signal voltage and a bias source 22 areconnected from I3 at the barrier to connection I3 by conductors l23, 24and 25. With N and P zones as shown in Fig. 1, the negative pole ofsource I8 is connected to the P zone and the positive pole to the Nzone.

The connection to the body at the barrier through the electrolyte I5 isa means of impressing a field at this barrier and parallel thereto, andis in the nature of a capacitative connection since there is substantialisolation between the electrolyte and the surface of the body.

The biasing source 22 is shown with its negative pole connected to thebarrier connection I6 since better results have been obtained with sucha connection. However, a positive bias may be used with good results.

A successfully operated device of this type was about 2 centimeterslong, 0.5 centimeter wide and 0.5 centimeter thick. 'I'he barrier wasabout midway between the end faces and substantially parallel to them.The bias voltages upon the electrodes i6 and lil relative to electrodeI3 were of the same order of magnitude, between 10 and volts.

Using devices like that of Fig. 1, a current change of a fewmicroamperes in the control circuit was made to produce a current changeof several milliamperes in the load circuit through Rr.. Thus currentamplication was obtained. The current gain was suiiicient to producepower amplification at the voltages used.

The device disclosed in Fig. 2 comprises two blocks or bodies and 3| ofinsulating material, such asa ceramic,VV with an electrode 32 inter- A39, respectively.

posedvbetween these blocks and electrodes 33 and'l A lm of P-typelelec-- suchas a copper-antimony alloyl or the 11F-type germaniumchanging it to N-type in. and 3l.`

a zone 35 between two P-type zones 36 The three zones are separated bybarriers 38 and ing antimony from the electrode 35 may be at about 650phosphorus from Phosphor same temperature.

32 into the zone C. and for diffusing bronze at about the as byregulating the time of the heat treatment, that the material at thesurface of the zone 35 opposite to that contacted by the electrode-32issubstantially neutral or only slightly N-type or, on the other hand,left as P-type. Following nomenclature which has been used for devicesof this type, the electrodes 32, 33 and 34 may be called respectively,base, emitter and co1- lector. applied to these and like electrodes inother figures to aid in understanding the structure. The device cf Fig.2 may be operated as an amplifier or control device by applying arelatively small positive bias, for example of the order of one volt,and a signal from sources such as battery 4I and signal source 42,respectively, to electrode 33 through input connections 43 and 44, thenegative side of the battery 4I being connected to the base electrode32. The outputcircuit includes a relatively high voltage source, forexample of voltage between 10 and 100 volts, such as battery with itsnegative pole connected to 34 and its positive pole to base electrode32. Included in this circuit is a load represented by a resistance RL.

If no P-type material remains in zone 35 the operation is as follows: Apositive or hole currentwill iiow into the P zone 3S under the iniiuenceof sources 4I and :22. The negative bias on the N zone 35 from batteryli injects electrons into this zone and reduces the impedance to holecurrent therethrough. The negative bias of battery 45 on electrode 3dthen causes a hole current toow to the output through electrode 34.Enough of the electrons and holes remain uncombined so that a controlanalogous to that in a three-electrode vacuum tube is obtained. Theinput current is in the direction of easy flow across the barrier 38 sothe impedance of this barrier thereto is relatively low. The outputcurrent is in the direction of diiiicult iiow through reversely op-4erated barrier 33 so the output is of high impedance. The output currentis comparable toi the input current but through a much higher impedance;therefore, the output power is higher than that at the input. A morecomplete explanation of the operation of this and the other devices willbe given subsequent to a description of the other embodiments o theinvention. If a thin layer of P-type material is left at the surfaceopposite to where 32 makes contact, the control eld will vary theeiective thickness of this layer to affect current iiow.

The device of Fig. 3 comprises a layer or Zone 5I of P-type material,such as germanium, interposed between two layers or lzones 52 and 53 of.

phosphorus bearbronze so that heat treatment will' The heat treatmentfor diffus-- The diifusing of the signifi-` cant impurity into the nlmmay be so controlled,Y

The designations B, E and C have Vbeen- N-'type material which also maybe germanium, separated` respectively by ybarriers 5B and 55.Connectionsare made to each'layer by electrodes 56, :5,1 and 5S,respectively, Which maybe termedv aszm'the-case of the device of Fig.2.v (56) emitter, (151)*ba'se, and (58) collector. These lelectrodesmaynbe,A formed as in the device of Fig. 1. The circuit connections aresimilar to those lin Fig. 2 with polarities reversed because of 'theinterchanging of N and P zones. In this device, the P layer i5| may bemade amenable to control by making it very thin, e. g., l 10q2centimeter -or less `or .only slightly of P-type or both. T heimpedanceof the Paone to electron flow will lbe low enough so vthatrintroduction of holes into the P zone fby the positivebias thereonvvill have a considerable control effect. Electrons may thus be made toilow with comparative ease through the P` zone..due `to Vthe eiect ofthe voltage on the base velectrode and will be drawn to the collector58and abstracted. Here as in the case 'of Fig. 2. in one way of,operation, the input vis of loW impedance, the output of high impedance,and the input and output currents comparable with resultingA poweramplification.

In Fig. 4 there is shown a device similar tothe onein Fig. 3 but with adifferent means for connecting-to the intermediate zone ofsemiconducti-ve material. In this modification. the P zone El' isinterposed between N zones 62 and 63. A metallic grid, .sections ofwhich are shown at y|54, is :embedded inthe P zone and has a projectingportion |5-to which external connection may be made. This grid serves asthe base electrode. The emitter and `collector electrodes 6B and 61respectively, and the respective N zones are simi.- lar to those in thedevice of Fig. 3. This device maybe operated like the device of Fig. 3with appropriate connections to the emitter, base-andv collectorelectrodes.

The fractional View, Fig. 5, shows a portion of a device similar to thatof Fig. 4 with modifications in detail.v In order to insure a good,substantially ohmic contact between the electrodes and thevsemiconductive material, a relatively thin layer of the semiconductivematerial adjacent each electrode is made of material having a higherconcentrationof significant impurities of the Atype characterizing thatconductivity type. These high 4impurity layers will have higherconductivity than the rest of the semiccnductive mate rial in the givenzone and thus less tendency toward barrier formation at theelectrode-semiconductor interface. These layers are B8, E9, and 1.0 forthe emitter, base (grid), and collector electrode, respectively. Suchhigh impurity layersmay beused in the other embodiments of theinvention.

In order to shield `the grid or base electrode 64- from the effects ofthe field of the emitter, a

layerof insulation 1|, .is applied to the side of the.

gridxfacing the emitter electrode. The ilow of charge carriers is thusdirected through the grid between its conductors.

Thedevice shown in Fig. 6 is similar to thel one shown in Fig. Swith alayer 53a of reduced extent allowingatcontact 51a on a. face of the Player 5|.

In Fig. 'J there are shown a plurality of assembledi semiccnductivelayers or slabs |.|.0 to I |-3, inclusive. An insulator slab ||4 isincluded in place of part of the intermediate P layer and the N layer onthe collector side is tapered `toward theinsulator to reduce sidewiseiiow of electrons therein and thus 4path4 length from 2B to the- N.layer on-,the collectorl side.

lli

vAdditional functions may lbe performed by Adevices containing morelayers and electrodes. Fig. 8 yshovvsfa configuration which may be usedas a mixer'or converter. Five layers-or zones 9| to 95, inclusive, areshown which are alternately N and P. ALayers 9| and 95 are similar tothev 'L to 96, 91 and 99, 98 being regarded as grounded.

This. function will be non-linear in the voltages and will containquadratic terms involving prodnets-of the voltages on 96 and 91. Theseproduct terms` -will play. the, same role as in other nonlinear mixersor converters and will lead to collector current ycomponents havingfrequencies whichqare combinations of those applied to 96 and 91.

The voltages may be applied respectively to 96 and 91 from sources |0|,|04 and |02, |05, these being bias and signal voltages as indicated. Thesignal voltages could be from a local oscillator andan incoming` signal,for example, or be other signals to be mixed. The output is taken from|06 and |01 and source |0-3 provides the collector bias. Lc and CB areisolating chokes and blocking condensers, respectively.

I-nvFig. v9 a device like that in Fig. 8 is provided with an additionalelectrode |08 on the middle N region and arranged so that layers 9|, 92and 93 with suitable connections as shown comprise an oscillator. Theinput is applied to layer 94 and the mixed output taken from |06 and|01. The sources of energy correspond tc those in Fig. 8 with source|.09added as the collector bias for the oscillator section. Lm and CT aretuning elements ofthe oscillator section, Le and CB are the chokes andblocking condensers and T the coupling transformer.

nladdition to the voltage and thus power amplification which may beobtained with devices of this type, current amplication may be obtainedby setting Aup at the collector electrode a condition similar to that.required for rectification. rhis may be done by makingV the collectorelectrode a rectilier .Contact of the point or large area type ratherthana substantially ohmic contact. Another way of doing this is to leavethe actual contact Aat thev electrode ohmic and to introduce a smallregionv of opposite type material tothatofthe-collector Zone around thecollector electrode. For example, in a device like that of Fig. 3.a zoneof P-type material may be introduced 'betweenthe collector electrode 53and the N zone 53, as shown in Fig. 3A or, as shown in Fig. 3B, a-pointcontact 8| may be substituted Vfor electrodeV 58er electrode 58 may beapplied in a manner to set up a barrier. With collector connections of`this type, the output current may be made greater than the inputcurrent as will be subsequently explained.

Structures similar to those described but havingonly. two electrodes canbeused as negative resistance elements at very high frequencies makinguse of transit time effects. Fig. l0 represuch-a device. It comprisesthree substantiallyY parallel layers Ne, P and Nc, of alternatingimpurity content with. twometal electrodes, one at either side. In. theexample shown, the conductivity is; supposed to be entirely due toelectrons.

, phase with the voltage the voltage on Va. y impedance of the device asviewed looking in on Increase V3 and the actual iiow of electrons from Pto Nc. As a consequence of this, the electron current flowing between Pand NC will be out of V3. With the type of structure shown, this phaselag will be sufcient to that the current ilowing between P and Nc can bemade more than 90 degrees out of phase with Under these conditions thethe V3 terminal will exhibit negative resistance.

The theory of somewhat related electronic devices involving negativeresistance due to transit time is known in the literature. See forexample Bell System Technical Journal, January 1934 (vol. 13), and`October 1935 (vol. 14). In order for such devices to operate it isnecessary that the transit response for a change in voltage on V3 have asuitable characteristic. The principal requirement of thischaracteristic is that the buildup in current following the change in V3should occur with a certain delay after the change in Va. In the type ofdevice shown in Fig. 10, this desired feature will occur automatically.The reason for this is that electrons drift relatively slowly throughthe P region, whereas they will traverse the P to Nc gap rapidly becauseof the high electric field present there. As a consequence of this,electrons which iiow from Ne to P during one phase of V3 carry theirprincipal current from P to Nc at a later time and can thus be made toflow more than 90 degrees out of phase with the voltage applied to V3and in this way furnish negative resistance.

These eii'ects may be further enhanced by use of a structure of the formshown in Fig. having a barrier as illustrated by the diagram Fig.

10b. This shows a situation at the collector similar to that describedearlier in connection with Figs. 3A and 3B. In this case there is abarrier for electron ow from Ne to C. Electrons ac cumulating in thepotential minimum to the left of C will enhance hole flow from C back toP and hence to E. Transit time effects will occur both in the electronnow from P to Nc and in the dcvelcpment of a potential difference acrossthe A barrier in front of C due to electron accumulation and to holetransit time through the Nc region. These eects can again be utilized toproduce a negative resistance for the device at a frequency properlyadjusted to the over-all efiective transit time and the shape of thecurrent response curve.

It is believed that a logical explanation of the operation of devicesmade in accordance with this invention may be given with respect to adevice like that of Fig. 3. Although the electrical currents of interestin semiconductors are, according to theory, carried by electrons, it isalso well known in accordance with such theory that the electrons maycarry the current either by the excess process, called conduction byelectrons, or by the defect process, called conduction by holes.

For purposes of explanation, consideration will be given to hcw twoprocesses of conduction by electrons enables a conventional vacuum tubeto operate. In the vacuum tube case, the two processes are (1) metallicconduction and (2) thermionic emission followed by ilow through space.When the voltage on the grid of the tube is changed, its charge ischanged by a now of current into its leads and wires by metallicconduction. This charge exerts a eld which attracts or repels thethermionic electron space charge about the cathode and thus the spacecurrent passing through the grid to the plate. An important and usefulfeature of a vacuum tube is that these two currents do not become mixed;the high work function and low temperature of the grid wires prevent themetallic conduction current from escaping from the grid and iiowing tothe plate. The fact that the grid is negative with respect to thecathode prevents the space current from reaching the grid. Thus the :dowof electrons by metallic conduction in the grid controls the spacecurrent from cathode to plate. However, practically no power is consumedby the grid since its charging current is separated fromthe spacecurrent which it controls. This discussion, which neglects` someelements of vacuum tube theory (such as displacement currents, transittime eects, etc.) will serve as a basis for indicating how the twoprocesses of conduction in semiconductors may eiect a similar usefulcontrol of one form of current by another.

In Fig. 11 there is shown a representation of a semiconductor structurewhich is analogous to a three-electrode vacuum tube. In this figure,diagrams a, c and d show the energies of electrons in the lled andconduction bands in the semiconductor in the customary way. The physicalstructure of the semiconductor is represented at e and consists or"three regions of semiconductor with connecting electrodes correspondingto the cathode, grid and plate of a vacuum tube as shown at f. Thediierent parts of the semiconductor are in intimate contact, so thatthere are no surface states (such .as occur on the free surfaces ofsemiconductors) or other major imperfections at the boundaries. riheprincipal variation in properties should arise from the varyingconcentration of impurities as shown at b which represents theconcentration of donors minus the concentration of acceptors.

In oi, there are no potentials applied to the electrodes and the Fermilevel is independent of position. (The Fermi level, sometimes called thechemical potential for electrons, is the parameter e in the Fermi-Diracdistribution function f=1/[l+exp(E-e/kT)l. It can be interpreted as apotential by dividing by the charge on the carrier, in this case thenegative charge of the electron.) For the case illustrated, theconductivity in the N layers is due to electrons and in the P layer toholes. The diagram has been drawn to shown a much higher electronconcentration in N than holes in P. In fact, the N concentration is sohigh that a degenerate gas is formed as in a metal.

If electrodes E and B (diagram e of Fig. 1l) are maintained at apotential V1 and C is made more positive to a potential V2, thesituation shown in diagram c occurs. This corresponds to applyingvoltage in the reverse direction across the Nc-P junction of diagram e.In this case,

- small current flows because the voltages are such which is present.`As a result the maximum in P and ow to "the: conduction'l bandandy(except for the. degen- "erate case) the'numberof Acarriers'decreases asexp-qAV/lcT) where AV is the spacing between the Fermi level andthe bandconcerned, and q is the electronic charge. As a consequence of the smallnumber of holes in the Nc region. and Ielectrons in the P region, verysmall currents flow across the barrierfand the reverse direction hashigh resistance.

In diagram d ofFig. 11,theadditional effect of applying a voltage intheforward direction across theNe-P or left-hand barrier is shown.'Thisis the forward direction for this barrier, and electronstend toflow fromsNe to P. This current builds up exponentially with the voltagediffer- -ence between'Vi-and V2. At the same timefholes -iiow from P to'-i\ e. However, for the structure shown, the hole current willlbe muchsmaller than 'the 'electron current; the reason'for this 'beingessentiallythat since more electrons are available in'N@ thanlholesinPas Vdetermined 'by the configuration of the device, moreelectrons "Twoof these are illustrated in Fig.'12. vDiagrams 'a and b of this gurecorrespond'to equilibrium or zerov'current situations for `the deviceunder consideration. Under these conditions the number of holes inregion Ne is determined by the potentialenergy'diierenceUi. If apotential difference is applied between Neand P in theforwarddirectionacrossthe barrier as is shown inFig. 11D for example, then theconcentration ofholes in Ne due to flow from vl? will tend to `increaseexponentially with the voltage difference -Vz-'VL Similarly theconcentration ofelectrons 'flowing from Ne vto'vP will tend to increaselexponentially in the same way starting with a value `deter-mined by U2.Hence-if U2 is initiallyv less 'than Ui the tendency of' electrons toflow from Ne to P -will be lgreater than the tendency of 'holes to flowfromlP to Ne.

All of the cases considered in Figs. l1 and l2 are'designed so as toproduce this desirable f difference between U2 and U1. vlin' Figs. l1.and 12a this is accomplished by having diiierent concentrations ofimpurities in-Ne .and P in such a way `that the net concentration oftheelectrons inNe is greater than the concentration of holes `inP. In Figlithe lelectron concentration is so high that `a degenerate situationexists whereas in lig.v 12a a non-degenerate situation is shown. In Fig.12b this effect is urtherenhanced by using twoy differentsemiconductors. 'The semiconductor used for Nehas a :wider energy gapsince it is N-type. This increases the value of =U1 compared to U2 inthe P region. For example the Ne zone may be of N-type lsilicon and theother two zones ofP and N -type germanium re-A `spectively.

'If we idealize the structure for the moment and neglect any resistances`at the metal semi-conductor-contacts, and thehole current between '-P'and'Ne, the comparison between this device -and a vacuum' tubefbecomesclear. lthe grid, there is the P region, vwhich can be :charged inrespect to Ne by holes.

In place of This modulates the flow of electronsrom Ne into P .just asthe charge on the grid `modulates the iiow arises fromA several sources.

of electrons from the cathode. The vcharging current to P, consisting ofholes, does not flow lto Nc any more than does the charging current tothe grid. Thus the fact that there lare two Vprocesses of conductionthrough the P 1region permitscontrol to take place in a wayv similar'tothat in the vacuum tube.

`Before considering how the above description should be modied.whenneglected 'featuresare taken into account, consideration may begiven to the feature common to devices which amplify alternating-currentpower using a 'direct-current power supply. Such devices-have an input`.and an output circuit, and for purposes of'discussion may be regardedasv four terminal devices. Into the pair of input terminals there flowsdirectcurrent and alternating-current power (Pide and Pme) and into theoutput terminals'there'isa similar flow (Podcfand Pose). For a steadystate condition, the second law of thermodynamics requires that the sumor" all these powers is 'pesitive. VFor an amplier, however, Pm-lPfac isnegative, meaningthat the device gives -out alternating-current power.In a conventional circuit thepower is taken out between plate-andcathode and the alternating current and `voltage under operatingconditions arel like those 'of a negative resistance. That is, when theplatepotential swing' is negative'the plate current swing (i. e.,current into the tube, or electrons out) is positive. The reason forthis behavior is that the plate impedance is relatively high. Hence,when the grid swing is plus the plate current is increased over thedirect-current value and re- `mains increased even though Va negativeplate swing occurs. Hence, power can be delivered to the plate.

The Nc-P barrieracts in much the same way as the grid-,plate region ofthe vacuum tube. 'There is a steady reverse current;however,v this isrelatively insensitivevto plate potential. 'The electron current due tothe difference in potential between E and B, is alsorelatively'insensitive to collector voltage since once the electronshavepassed the maximum potential point in P they are practically certain tobe drawn to C. Hence the alternating current across the Nc-P barrier canbe made out of phase with-the voltage on C and output power Ycan bedelivered.

Next there may be taken into account the'fact -that there is actually acurrent flowing to 'B which may absorb input power. This current Holesfrom Ne will ow to P and also someholes from? will 'ow to Ne. Both ofthese currents tend to lower'the impedance of B and require more powerto drive it. Also, since B is positive vsome electrons'entering P tendto flow'to the electrodeB thus contributing still another source ofpower fabsorption. Holes and electrons will also combine in P at anenhanced rate compared'to thermal equilibrium because both the `hole andthe 'electron concentrations in P are appreciably greater than normal.This requires an additional hole current into P from B. However, propergeometrical requirements can be met so that these currents aresuiiiciently minimized to permit substantial power amplification.

The reason for this is that so long as the'P layer is not too thick, anappreciable fraction of the electrons flowing from Ne into P will continue to Nc. This means that the alternatingcurrent components ofcurrent in C will be comparable to the alternating currents in'E and B,Aswill be pointed out later, a properconi dition adjacent electrodedrawing is made as if Pc C may actually lead to largeralternating-current components in C than in either E or B. Furthermore,the impedance between E and B is relatively low since the Ne-P iunctionis operated in the forward direction.

Since power is IZR, and since the input and l output currents arecomparable but the output impedance is much higher, the output power isalso much higher.

Consideration will next be given to a further means of utilizing theseparability of the two conduction processes in semi-conductors in orderto increase the alternating current It at C compared to the current Ieat E and It at B. In

Fig. 13, diagram (a), the region just in front of the metal electrode Cis shown, as if a layer of P-type material Pc were inserted between Ncand C. This may be done by actually inserting a thin layer of P-typematerial between Ne and the electrode C or by replacing the electrode Cby a point contact such as has been shown in Fig. 3B. When the voltageon B is made positive, the Nc-Pc junction is operated in the forwarddirection. Hence, an appreciable fraction y of the current between Pcand Nc may be holes,4 and this fraction will increase if Pc is made moreP-type. For the eiects considered in this paragraph to be enhanced, ahole current from Pc into Nc and then to P is desirable. Hence the Nchad electrons. The advantage of this strucy ture is that it will lead toa multiplication of electron current arriving at the collector.

Diagram b in Fig. 13 shows the situation for no applied voltages on anenlarged scale with the electrons and holes depicted. In this case thenet hole current and electron currents are each `zero. In diagram c,Fig. 13, the situation is shown when an electron current is flowingV inl from P. In order for this current to iiow away to the right, thepotential hill between Nc and C must be reduced. This is accomplished byelectrons accumulating at X until their charge raises the potentialsufciently. They then ilow oiT to C. This shift-in potential alsoincreases the easiness with which holes from Pc can enter Nc and theniiow to P. 'I'he situation is entirely similar with the roles of holesand electrons reversed, to that at emitter. There the electron currentis increased by a charge of holes in the I P region. Here the holecurrent is increased by an accumulation of electrons in the Nc region.

Also, as before, the hole current may be much larger than the electroncurrent since more holes are available in this case.

Hence, a small electron current may induce a much larger hole current.

It is not necessary, however, for the layer PC to have an excess oiacceptors for the current enhancement discussed above to beaccomplished.

The essential feature is that the contact between the metal and the Neregion presents a smaller barrier for hole flow than for electron iiow.This can be accomplished as described above by adding a suiiicientnumber of acceptors to Pc. However, it will also occur if the contactbetween Cv and Nc has a suiiiciently high rectifying barrier,

. asis shown in Fig. 13D and which may be prol duced for example by useof a rectifying contact as in Fig. 3B. In this case electrons flowingfrom P will tend to accumulate to the left of the barrier until theyproduce a space charge which raises the potential energy Fig. 13C. Thischange in potential between Nc had more holes thanv for electrons, asinscale of the device.

Y combine with holes comparable to a `hole current from C to P asdescribed above.

By means of this process the alternating-current part of the current Itmay be made much larger than that of the current Ie and, consequently,the ratio of powers in the output and input circuits may be increased bycurrent amplication as well as by voltage amplification.

Certain limitations exist in regard to the dimensions of parts of theunits under discussion. These may be illustrated with respect to Figs. 3and 3A. Under operating conditions, a certain current will be drawn bythe P zone 5|. In order that the potential of 5| be substantiallyuniform, its resistance in the direction of current flow, namely frombase electrode 51 upwards in the figure, must not be too great. Foi' anygiven Width and conductivity in 5| this puts a limitation upon theminimum thickness, i. e., distance between barriers 54 and 55. Anotherclosely related requirement on the thickness is that it presents asubstantial resistance to electron flow from N zone 52 to N zone 53. Ifthe P zone is too thin, the space charge layer produced by operatingjunction 55 in the reverse direction will penetrate almost all of the Pzone, thus eliminating its holes and its desired conductivity parallelto the barrier.

A maximum limitation on the thickness of the P zone is established bythe recombination of holes and electrons. The P zone must not be so widethat electrons entering from the N zone 52 before passing through the Pzone and reaching the N zone 53. Experience with high-back-voltagegermanium indicates that distance at least as large as 10-2 centimetersare acceptable under this limitation, although smaller ones areadvantageous. A similar limitation is set by transit time effects. Inthe P `zone there will be electric fields tending to cause va, drift ofelectrons, also due to concentration gradients the electrons willdiffuse. Because of these effects a time will elapse between aA changein potential on 5| and the change in iiow of electrons from 5| to 53.An. additional time elapses before these electrons reach the additionalP zone (layer 85, Fig. 3A) and produce the hole flow back to 5|. If anyof these transit times are period of the impressed signal, loss inamplification will result.

The transit time and other capacitative eifects may be reduced byincreasing all acceptor and donator concentrations and reducing vthe Thegeneral trend of the behavior may be seen by arguments of a dimensionalcharacter. Thus if every linear dimension in the device is increased bya factor A is the new one, then the new potential at a point Aro, MIO,A20 is -"which #proves that the I'potential distribution .is simplymagnied in its linear extent to't-.the .newstructure. All-transit timeswill oe increased sbyraf factor of A2. Thisfollows fromthe fact that-vboththe` diffusion constant and themobility inzvolve the lengthdimension to the plus twopower, i. -le., crn/Seo. and cm.2/volt-sec. All`current densities increase as p times the electric iield .for`A driftcurrent, i. e., as A S, and as concentration gradient vior -diiiusioncurrent, i. e., as p/length or AM3. Hence all conductances per -.unit:area vary as A3. All capacities of N-P `junctions, etc., vary as 1/Aper unit area lso that tall lcharging ytime constants, capacity/conduc-:tanceavary as A2. :tained'ior the unitasfa-whole, since resistivity `islproportional to 1/ p or to A2 and resistance is :resistivity dividedbylength, the resistance of theA unitv varies as A. Theover-all capacityalso varies as A, again giving a time constant proportional to. A2.

The result of this analysis is thus that alltime constants vary as A2.if two units are produced, .differing by the scale'factor A asdescribed,` their :external impedances should vary as A and their:effective transit angles or the phase angles of .theirimpedances-should be equal at frequencies varying as A-2.

`llffects-of recombination oi electrons and holes :should not be alteredin an important way by the change .in scale. rThis follows from the factthat the probability per unit time of an electron combining -with ahole, either directly or by Ybeing -trapped `by a'doncr or acceptor, isproportional :to the concentration of holes, donors olf-acceptors, andhence'to `A-. Howeventhe time spent in .Qi-any :region is proportionalto A2. Hence the .probability of an electron, or hole, traversing a-certain layer without recombination is independ- Aent of A.

Thetemperature rise will depend on A. Asfsuming that the thermalconductivity is independent of the electrical conductivity, a situationwhich will be approximately true for semiconductors of reasonably highresistance, the ,thermal conductance of the unit will vary as A. Sincethe currents and consequently the power vary as A-l, the temperaturerise will vary as -A"2. This variation must be considered iin-,designingparticular units and may require operating small scale units at lessfavorable voltages than large scale units in order to reduce temper-I.ature rises. Any thermal time eiiects, as isvwell known from theory,and derivable as vabovefvary as A*2 and .thus change their frequencywith scale just as do the electrical eiiects.

This similitude theory shows that there will be great advantages indealing with materials ycontaining relatively high concentrations of do-'nor's or acceptors from the point of View of high frequency behavior.Even in principle, however, the change of scale cannot be pushedtoo far,because if the structures become too small, the essentially discretecharacter of the charge density becomes more important. Also themean-free path of the electron or hole becomes comparable with thethickness of the lay-ers. Also, for suiciently high concentrations,degenerate electron or hole gases will form. However, although thesewill modidfy the details of the argument, they will not invalidate theconclusion that operation at higher frequencies will result fromincreasing concentrations and decreasing scale.

There is a high degree of symmetry between the behavior of electrons andholes. (See for ex- 'Ihis same result may vbe obample, li'. Seitz,

'applicable vone type of a region of the other conductivitytype byvarying electrically vthe concentration of carriers normally present inthe-region.

It is to be understood that the speciiicembodimentsof theinventionshownand describedare but illustrative and that Yvariousmodications may be made therein vwithout departing from the scope andspirit of this invention.

Reference is made to application Serial No. 91,593, filed May 5, 1949,now PatentNo. 2,623,102 which discloses related subject-matter.

What is claimedis:

l. A signal translating device comprising .a body of semconductivematerial having. a plurality of successiveand contiguous Zones of.alternately opposite conductivity types, a circuit coupled to twosuccessive zones, means couplinga third zone whichis contiguous with oneof said two zones to said circuit todene ,an oscillator, and meansincluding other successive zones coupled to the output of saidoscillator. and defining a control element.

2. An intermodulating solid conductive device that comprises a bodyoisemiconductive material having a plurality of successive and contiguouszones .of alternately opposite conductivity types, a circuit coupled totwo successive zones, means coupling athird zone whichis contiguous withone of said two zones to said circuit to de- 'ine an oscillator, meansinterconnecting .other of said Zones one of whichis contiguous with oneof saidgroup of zonesto denneJ a control section, and an output circuitconnected ,to said control section.

` jacent thereto.

.prises means coupling said third zone tosaid second Zone to `deiineanoscillator with said first and second Zones.

5. An oscillator comprising a body of/semiconductive material havingtherein a first zone of one conductivity type between and contiguouswith two zones of the opposite conductivity type, a iirst circuitbetween said first zone and one of saidtwo zones, a second circuitconnected to said rst zone and the other .of said two Zones-,anda

' coupling between said irst. and second circuits.

6. An oscillator in accordance with claim 5 wherein said body includes afourth zone contiguous with one of said two zones and of said oneconductivity typ-e and a fth zone contiguous with said fourth zone andof said opposite conductivity type,the^oscillator including alsoa load l7 circuit connected to said fth zone and a control circuit connected tosaid fourth zone.

7. A signal translating device comprising a body oi semiconductivematerial having a rst and a third zone of one conductivity type and asecond zone of the opposite conductivity type intermediate andcontiguous with said first and third Zones, an input circuit connectedto said irst and second zones, a feedback coupling between said thirdzone and said input circuit, and means for deriving an output from saiddevice.

8. An oscilator comprising a body of semiconductive material having arst and third zone of one conductivity type and a second zone ofopposite conductivity type intermediate and con- References Cited in thele of this patent UNITED STATES PATENTS Number Name Date 1,949,333 WeberFeb. 27, 1934 2,328,440 Esseling et a1 Aug. 3l, 1943 2,428,400 Van Geetet a1 Oct. 7, 1947 2,502,479 Pearson et a1. Apr. 4, 1950

